Figure shown a \(DC\) voltage regulator circuit, with a Zener diode of breakdown voltage \(= 6\,V\). If the unregulated input voltage varies between \(10\, V\) to \(16\, V\), then what is the maximum Zener current ?.......\(mA\)

When zener diode works in breakdown state, voltage across the zener will remain same.

\(\therefore \) \({V_{{\text{across}}}}4{\mkern 1mu} K\Omega  = 6{\text{V}}\)

\(\therefore \) Current through \(4\, K\Omega = \frac{6}{4000}\,A\) \(=\frac{6}{4}\,mA\)

since input voltage \(=16\,V\)

\(\therefore \) Potential difference across \(2 \mathrm{K} \Omega=10 \mathrm{V}\)

\(\therefore \) Current through \(2 \mathrm{k} \Omega=\frac{10}{2000}=5 \mathrm{mA}\)

\(\therefore \) Current through zener diode \(=\left(I_{s}-\mathrm{I}_{\mathrm{L}}\right)=3.5 \mathrm{mA}\)